cfg80211/mac80211: better channel handling

Currently (all tested with hwsim) you can do stupid
things like setting up an AP on a certain channel,
then adding another virtual interface and making
that associate on another channel -- this will make
the beaconing to move channel but obviously without
the necessary IEs data update.

In order to improve this situation, first make the
configuration APIs (cfg80211 and nl80211) aware of
multi-channel operation -- we'll eventually need
that in the future anyway. There's one userland API
change and one API addition. The API change is that
now SET_WIPHY must be called with virtual interface
index rather than only wiphy index in order to take
effect for that interface -- luckily all current
users (hostapd) do that. For monitor interfaces, the
old setting is preserved, but monitors are always
slaved to other devices anyway so no guarantees.

The second userland API change is the introduction
of a per virtual interface SET_CHANNEL command, that
hostapd should use going forward to make it easier
to understand what's going on (it can automatically
detect a kernel with this command).

Other than mac80211, no existing cfg80211 drivers
are affected by this change because they only allow
a single virtual interface.

mac80211, however, now needs to be aware that the
channel settings are per interface now, and needs
to disallow (for now) real multi-channel operation,
which is another important part of this patch.

One of the immediate benefits is that you can now
start hostapd to operate on a hardware that already
has a connection on another virtual interface, as
long as you specify the same channel.

Note that two things are left unhandled (this is an
improvement -- not a complete fix):

 * different HT/no-HT modes

   currently you could start an HT AP and then
   connect to a non-HT network on the same channel
   which would configure the hardware for no HT;
   that can be fixed fairly easily

 * CSA

   An AP we're connected to on a virtual interface
   might indicate switching channels, and in that
   case we would follow it, regardless of how many
   other interfaces are operating; this requires
   more effort to fix but is pretty rare after all

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 132 insertions, 39 deletions

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index c27bef8e0c11..ec1b4a896c6e 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -588,6 +588,7 @@ static int nl80211_send_wiphy(struct sk_buff *msg, u32 pid, u32 seq, int flags,
                 i++;
                 NLA_PUT_U32(msg, i, NL80211_CMD_SET_WIPHY_NETNS);
         }
+        CMD(set_channel, SET_CHANNEL);
 
 #undef CMD
 
@@ -688,10 +689,90 @@ static int parse_txq_params(struct nlattr *tb[],
         return 0;
 }
 
+static bool nl80211_can_set_dev_channel(struct wireless_dev *wdev)
+{
+        /*
+         * You can only set the channel explicitly for AP, mesh
+         * and WDS type interfaces; all others have their channel
+         * managed via their respective "establish a connection"
+         * command (connect, join, ...)
+         *
+         * Monitors are special as they are normally slaved to
+         * whatever else is going on, so they behave as though
+         * you tried setting the wiphy channel itself.
+         */
+        return !wdev ||
+                wdev->iftype == NL80211_IFTYPE_AP ||
+                wdev->iftype == NL80211_IFTYPE_WDS ||
+                wdev->iftype == NL80211_IFTYPE_MESH_POINT ||
+                wdev->iftype == NL80211_IFTYPE_MONITOR;
+}
+
+static int __nl80211_set_channel(struct cfg80211_registered_device *rdev,
+                                 struct wireless_dev *wdev,
+                                 struct genl_info *info)
+{
+        enum nl80211_channel_type channel_type = NL80211_CHAN_NO_HT;
+        u32 freq;
+        int result;
+
+        if (!info->attrs[NL80211_ATTR_WIPHY_FREQ])
+                return -EINVAL;
+
+        if (!nl80211_can_set_dev_channel(wdev))
+                return -EOPNOTSUPP;
+
+        if (info->attrs[NL80211_ATTR_WIPHY_CHANNEL_TYPE]) {
+                channel_type = nla_get_u32(info->attrs[
+                                   NL80211_ATTR_WIPHY_CHANNEL_TYPE]);
+                if (channel_type != NL80211_CHAN_NO_HT &&
+                    channel_type != NL80211_CHAN_HT20 &&
+                    channel_type != NL80211_CHAN_HT40PLUS &&
+                    channel_type != NL80211_CHAN_HT40MINUS)
+                        return -EINVAL;
+        }
+
+        freq = nla_get_u32(info->attrs[NL80211_ATTR_WIPHY_FREQ]);
+
+        mutex_lock(&rdev->devlist_mtx);
+        if (wdev) {
+                wdev_lock(wdev);
+                result = cfg80211_set_freq(rdev, wdev, freq, channel_type);
+                wdev_unlock(wdev);
+        } else {
+                result = cfg80211_set_freq(rdev, NULL, freq, channel_type);
+        }
+        mutex_unlock(&rdev->devlist_mtx);
+
+        return result;
+}
+
+static int nl80211_set_channel(struct sk_buff *skb, struct genl_info *info)
+{
+        struct cfg80211_registered_device *rdev;
+        struct net_device *netdev;
+        int result;
+
+        rtnl_lock();
+
+        result = get_rdev_dev_by_info_ifindex(info, &rdev, &netdev);
+        if (result)
+                goto unlock;
+
+        result = __nl80211_set_channel(rdev, netdev->ieee80211_ptr, info);
+
+ unlock:
+        rtnl_unlock();
+
+        return result;
+}
+
 static int nl80211_set_wiphy(struct sk_buff *skb, struct genl_info *info)
 {
         struct cfg80211_registered_device *rdev;
-        int result = 0, rem_txq_params = 0;
+        struct net_device *netdev = NULL;
+        struct wireless_dev *wdev;
+        int result, rem_txq_params = 0;
         struct nlattr *nl_txq_params;
         u32 changed;
         u8 retry_short = 0, retry_long = 0;
@@ -700,16 +781,50 @@ static int nl80211_set_wiphy(struct sk_buff *skb, struct genl_info *info)
 
         rtnl_lock();
 
+        /*
+         * Try to find the wiphy and netdev. Normally this
+         * function shouldn't need the netdev, but this is
+         * done for backward compatibility -- previously
+         * setting the channel was done per wiphy, but now
+         * it is per netdev. Previous userland like hostapd
+         * also passed a netdev to set_wiphy, so that it is
+         * possible to let that go to the right netdev!
+         */
         mutex_lock(&cfg80211_mutex);
 
-        rdev = __cfg80211_rdev_from_info(info);
-        if (IS_ERR(rdev)) {
-                mutex_unlock(&cfg80211_mutex);
-                result = PTR_ERR(rdev);
-                goto unlock;
+        if (info->attrs[NL80211_ATTR_IFINDEX]) {
+                int ifindex = nla_get_u32(info->attrs[NL80211_ATTR_IFINDEX]);
+
+                netdev = dev_get_by_index(genl_info_net(info), ifindex);
+                if (netdev && netdev->ieee80211_ptr) {
+                        rdev = wiphy_to_dev(netdev->ieee80211_ptr->wiphy);
+                        mutex_lock(&rdev->mtx);
+                } else
+                        netdev = NULL;
         }
 
-        mutex_lock(&rdev->mtx);
+        if (!netdev) {
+                rdev = __cfg80211_rdev_from_info(info);
+                if (IS_ERR(rdev)) {
+                        mutex_unlock(&cfg80211_mutex);
+                        result = PTR_ERR(rdev);
+                        goto unlock;
+                }
+                wdev = NULL;
+                netdev = NULL;
+                result = 0;
+
+                mutex_lock(&rdev->mtx);
+        } else if (netif_running(netdev) &&
+                   nl80211_can_set_dev_channel(netdev->ieee80211_ptr))
+                wdev = netdev->ieee80211_ptr;
+        else
+                wdev = NULL;
+
+        /*
+         * end workaround code, by now the rdev is available
+         * and locked, and wdev may or may not be NULL.
+         */
 
         if (info->attrs[NL80211_ATTR_WIPHY_NAME])
                 result = cfg80211_dev_rename(
@@ -748,26 +863,7 @@ static int nl80211_set_wiphy(struct sk_buff *skb, struct genl_info *info)
         }
 
         if (info->attrs[NL80211_ATTR_WIPHY_FREQ]) {
-                enum nl80211_channel_type channel_type = NL80211_CHAN_NO_HT;
-                u32 freq;
-
-                result = -EINVAL;
-
-                if (info->attrs[NL80211_ATTR_WIPHY_CHANNEL_TYPE]) {
-                        channel_type = nla_get_u32(info->attrs[
-                                           NL80211_ATTR_WIPHY_CHANNEL_TYPE]);
-                        if (channel_type != NL80211_CHAN_NO_HT &&
-                            channel_type != NL80211_CHAN_HT20 &&
-                            channel_type != NL80211_CHAN_HT40PLUS &&
-                            channel_type != NL80211_CHAN_HT40MINUS)
-                                goto bad_res;
-                }
-
-                freq = nla_get_u32(info->attrs[NL80211_ATTR_WIPHY_FREQ]);
-
-                mutex_lock(&rdev->devlist_mtx);
-                result = rdev_set_freq(rdev, NULL, freq, channel_type);
-                mutex_unlock(&rdev->devlist_mtx);
+                result = __nl80211_set_channel(rdev, wdev, info);
                 if (result)
                         goto bad_res;
         }
@@ -864,6 +960,8 @@ static int nl80211_set_wiphy(struct sk_buff *skb, struct genl_info *info)
 
  bad_res:
         mutex_unlock(&rdev->mtx);
+        if (netdev)
+                dev_put(netdev);
  unlock:
         rtnl_unlock();
         return result;
@@ -3561,9 +3659,8 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 {
         struct cfg80211_registered_device *rdev;
         struct net_device *dev;
-        struct wireless_dev *wdev;
         struct cfg80211_crypto_settings crypto;
-        struct ieee80211_channel *chan, *fixedchan;
+        struct ieee80211_channel *chan;
         const u8 *bssid, *ssid, *ie = NULL, *prev_bssid = NULL;
         int err, ssid_len, ie_len = 0;
         bool use_mfp = false;
@@ -3606,16 +3703,6 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
                 goto out;
         }
 
-        mutex_lock(&rdev->devlist_mtx);
-        wdev = dev->ieee80211_ptr;
-        fixedchan = rdev_fixed_channel(rdev, wdev);
-        if (fixedchan && chan != fixedchan) {
-                err = -EBUSY;
-                mutex_unlock(&rdev->devlist_mtx);
-                goto out;
-        }
-        mutex_unlock(&rdev->devlist_mtx);
-
         ssid = nla_data(info->attrs[NL80211_ATTR_SSID]);
         ssid_len = nla_len(info->attrs[NL80211_ATTR_SSID]);
 
@@ -5185,6 +5272,12 @@ static struct genl_ops nl80211_ops[] = {
                 .policy = nl80211_policy,
                 .flags = GENL_ADMIN_PERM,
         },
+        {
+                .cmd = NL80211_CMD_SET_CHANNEL,
+                .doit = nl80211_set_channel,
+                .policy = nl80211_policy,
+                .flags = GENL_ADMIN_PERM,
+        },
 };
 
 static struct genl_multicast_group nl80211_mlme_mcgrp = {